As an example of conventional floor structures for vehicle bodies, a floor structure including a seat bracket extending in a vehicle width direction for mounting a seat above a floor panel is disclosed in, e.g., Japanese Patent Application Laid-Open Publication No. 2006-82720 (JP 2006-82720 A).
FIG. 8 hereof shows the floor structure for a vehicle body disclosed in JP 2006-82720 A.
A floor panel 101 shown in FIG. 8 is comprised of a center tunnel 102 extending in the longitudinal direction through the region disposed centrally with respect to the vehicle width, and floor panel parts 103, 103 provided to the left and right of the center tunnel 102. The rear parts of the floor panel parts 103, 103 are seat-mounting positions 104. At the rear ends of the floor panel parts 103, 103, a kick-up part 106 rising as high as the center tunnel 102 is formed.
Side sills 107, 107 are provided on the external edges of the respective floor panel parts 103, 103; and front seat brackets 111, made to extend in the vehicle width direction and used to mount the front part of the seat, are provided so that both ends thereof are mounted between the side surfaces of the center tunnel 102 and the inside surfaces of the side sills 107, and the bottom surfaces are mounted on the floor panel parts 103. Rear seat brackets 112, made to extend in the vehicle width direction and used to mount the rear part of the seat, are provided so that both ends thereof are mounted between the side surfaces of the center tunnel 102 and the inside surfaces of the side sills 107, the bottom surfaces are mounted to the floor panel parts 103, and the rear surfaces are mounted to the kick-up part 106.
It is difficult to ensure sufficient rigidity in the joined parts, because only the inside ends of the front seat brackets 111 and the rear seat brackets 112 are bonded to the side surfaces of the center tunnel 102. The rigidity of the joined parts will be described with reference to FIGS. 9, 10A and 10B showing a separate but similar floor structure.
Referring to FIG. 9, a floor panel 121 is comprised of a tunnel part 122 and floor bodies 123, 123 formed on the left and right of the tunnel part 122. Side sills 125 extending longitudinally are mounted on the respective outside edges of the floor bodies 123, 123. Front cross members 126 used to mount the front part of the seat and rear cross members 127 used to mount the rear part of the seat are provided so that both ends thereof extend between the side surfaces of the tunnel part 122 and the inside surfaces of the side sills 125, and the bottom parts are mounted to the floor bodies 123.
Reference is made next to FIGS. 10A and 10B showing in cross section the floor structure of FIG. 9.
An internal cross member 128 extending in the vehicle width direction is mounted to the inside surfaces on the inside of the tunnel part 122, as shown in FIG. 10A. A reinforcing member 131 is mounted to the bottom surfaces of the left and right floor bodies 123, 123.
The front cross members 126 are simply bonded to the outside surfaces of the tunnel part 122 as shown in FIG. 10B, and since the internal cross member 128 is merely also simply bonded to the inside surfaces of the tunnel part 122, the bonded portions at the borders between the closed cross sections formed below the front cross members 126 and the closed cross section formed above the internal cross member 128 are fragile parts having low strength and rigidity.
As a result, in FIG. 10A, when the floor panel 121 vibrates vertically along with the vertical vibration of the vehicle body, the floor panel 121 readily undergoes severe vibration so as to bend, as shown by the arrows, relative to the joined parts between the tunnel part 122 and the front cross members 126 and the joined parts between the tunnel part 122 and the internal cross member 128.